1. Field of the Invention
This invention relates to an injector mounting structure for mounting injectors on a cylinder head of an engine, especially, a direct injection engine.
2. Description of the Invention
It has been demanded in recent years that, mainly, a miniaturized diesel engine is formed to a DOHC and multi-valve structure having two cam shafts per cylinder and two suction valves or exhaust valves per cam shaft so that such a diesel engine meets the necessary conditions of having a high output, a low fuel consumption and a capability of following the exhaust gas regulations. There is a known engine of this kind (Japanese Patent Laid-Open No. 261114/1996) in which injectors, the number of which corresponds to that of cylinders, are provided in a cylinder head so as to extend to substantially central portions of the cylinders, two cam shafts extending in parallel with each other so as to sandwich the injectors being provided in the cylinder head, the injectors being provided between two cams for suction valves or two cams for exhaust valves which are mounted on their respective cam shafts.
Each of the injectors disclosed in the above-mentioned publication is provided in a vertically extending state between two cam shafts. An upper end portion of the injector projects to a position above a cylinder head cover, and a fuel supply pipe and a fuel return pipe are connected to this projecting upper end portion. Since the injectors are of a vertically extending type, a total height of the engine becomes large, so that the engine requires a large space. When the total height of the engine is large, a space necessary for disposing fuel pipes connected to the injectors also becomes large.
In a structure in which injectors are projected from a head cover with joint portions for fuel pipes, such as fuel supply pipes and fuel return pipes provided at the upper ends thereof, it is necessary that the portions of the fuel supply pipes which are in the vicinity of the joint portions of the injectors be bent so as to prevent the fuel supply pipes from interfering with other constituent parts. However, there is a limit to a bend radius of the high-pressure fuel supply pipes, so that the high-pressure fuel pipes have to be gently bent. To meet the requirements, it is necessary that a sufficient spatial margin be provided between the fuel pipes and other constituent parts. When a fuel injection pump is fixed to a side portion of an engine, the length of the fuel supply pipes connecting the fuel injection pump and the joint portions mentioned above together becomes large.
Since the long fuel pipes have a high passage resistance of a fuel passing therethrough, a response delay of fuel injection is liable to occur, and the engine performance and exhaust gas characteristics would be deteriorated.
In a miniaturized direct injection diesel engine having small cylinder bore diameter, valve stems are necessarily formed so that the valve stems are positioned close to and incliningly with respect to injectors unless it is possible that the positions of the ports of suction and exhaust valves with respect to combustion chambers are set close to each other as these ports are kept perpendicular to a port-opened wall surface, in other words, unless it is possible that cam shafts on which valve driving cams are mounted are provided close to each other as the cam shafts are kept parallel to the injectors. In such a structure, the valve ports are opened diagonally with respect to the combustion chambers, and, when the angle of inclination of the valve ports is large, the engine performance is deteriorated as a natural consequence. It is conceivable that the joint portions between the injectors and fuel pipes are provided simply on one side of the injectors so as to solve the above-mentioned problems which arise when the joint portions of the fuel pipes with respect to the injectors are provided on the upper ends of the injectors. However, when the joint portions of the injectors, which are provided between parallel cam shafts positioned above the cylinder head, and also between the cams for the suction and exhaust valves mounted on these cam shafts, with respect to the fuel pipes are simply provided on one side of the injectors, the cam shafts and fuel passage bosses interfere with each other. When any measures are taken in order to prevent this interference, another problem that a distance between the cam shafts increases instead occurs.
Since a distance between the valve ports of the suction and exhaust valves is fixedly set in accordance with the type of the engine, the valve stems incline, when a distance between the cam shafts increases, with respect to the axis of the injector. In such a structure of the valve ports opened in a combustion chamber, an excellent engine performance cannot be expected. Therefore, it is desired that consideration be given to the correlation in the injector mounting structure between the fuel passage in the injector and an arrangement for preventing the interference of the fuel passage boss and cam shafts with each other, so as not to cause the deterioration of the performance of a miniaturized diesel engine as well.